Douluo: I Just Made Everything Up - Chapter 11: The Gap In Realm

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.

The light is here because the darkness exists. Just like that, the human realm exists because the demon realm is here. And in the great palace of the Blade Empire, a crown touches the peak of its glory before it falls from its grace. Lush Von Blade was the royal crown prince of one of the greatest empires on the southern continent. He is loyal but betrayed.On the other hand, where even the Gods fear to set a foot on, a demon lord abides. His grace and cruelty have been unseen for centuries. He is the supremacy in the three realms. While Lush is the light, he is the darkness. Each exists because the other is here.

The Demon King dies and the entire Demon Realm perishes in the prologue of “The Demon King is Dead,” and I have become the Demon Prince of that novel.

… Somebody save me.

……………………………………………………………

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After Chuzheng is suddenly pronounced dead by a system all of a sudden, her only worry in life becomes—spending money. Ever since she gets stuck with this system, her back is no longer sore and her legs no longer ache. Heck, there isn’t even a time when she goes out of breath.System: Let us set a small goal first and squander a hundred million… Little Miss, stop right there! Don’t activate the invincible mode!(▼皿▼#) Chuzheng: Can you please explain what is this thing that is leeching off me?Random Thing: Babe, you can do whatever you want to me.Chuzheng: (touches her blade) In-In that case, I will not stand on ceremony.System: Little Miss, please put the saber down right this instant! (▼へ▼メ)#LittleMissAlwaysDoesAsShePleases.